1. Technical Field
The disclosure relates to a secondary battery, more particularly, to a secondary battery in which a shock absorbing portion is formed near a vent formed on a wider side of a can so as to protect the vent from the damage by an external shock.
2. Description of the Related Art
In general, unlike primary batteries, which are not chargeable, secondary batteries are chargeable and dischargeable, and consequently, are widely used in a variety of high-tech electronic devices such as cellular phones, notebook computers, camcorders, and the like. Particularly, a lithium secondary battery has an operating voltage of about 3.6V, which is three times higher than that of a nickel-cadmium battery or a nickel-hydrogen battery. In addition, a lithium secondary battery has a high energy-density per unit weight. Accordingly, it shows a tendency to expand rapidly.
A typical lithium secondary battery uses lithium oxide as a positive electrode active material and a carbon material as a negative electrode active material. In addition, lithium secondary batteries can be formed in a variety of shapes, for example, cylinders, squares, or pouch shapes.
Of the shapes mentioned above, a square-type secondary battery includes an electrode assembly, a can receiving the electrode assembly, and a cap assembly coupled to the can. The electrode assembly includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and negative electrode, and a positive electrode tab and a negative electrode tab, which protrude from the positive electrode and the negative electrode, respectively.
The can is a metal container in a rectangular shape, and is manufactured by a processing method such as deep drawing. Accordingly, the can itself can function as a terminal. Preferably, the can is made of aluminum or aluminum alloy, which is a light-weight conductive metal. The can is a container for the electrode assembly and an electrolyte, and its open upper part, through which the electrode assembly is inserted, is sealed by the cap assembly.
The cap assembly includes a cap plate coupled to the upper part of the can, an electrode terminal installed through a terminal through-hole, an insulating plate installed at the lower surface of the cap plate, and a terminal plate through which an electric current is applied as the electrode terminal is installed on the lower surface of the insulating plate. A gasket is disposed between the electrode terminal and the terminal through-holes. A negative electrode of the electrode assembly is coupled to the electrode terminal through the negative electrode tab and the terminal plate, and a positive electrode of the electrode assembly is coupled to the cap plate or the can through the positive electrode tab.
A vent can be formed on one side of the cap plate or on a wider side of the can. The vent is designed to rupture preferentially over other parts of the can or cap in order to discharge internal gas when the internal pressure of the battery increases due to overcharge and the like, thereby maintaining the physical integrity of the battery. The vent formed on the wider side of the can, hereinafter, referred to as a side vent, comprises an opening of a predetermined thickness.
However, a conventional side vent has several drawbacks. In general, the thickness of a can is about 0.3 mm, and the thickness of the opening of a side vent is barely about dozens of micrometers. Primarily, internal gas pressure in the battery preferentially ruptures the vent opening instead of another part of the can or cap assembly, thereby confining the contents of the battery in the can. However, the opening of the vent is so thin that it can be cracked or ruptured by a slight external shock. That is to say, the reliability of the battery can be compromised if the vent is damaged.